Because vitamin D deficiency is associated with obesity, Mason and colleagues hypothesized that vitamin D3 supplementation (2000 IU daily) in overweight/obese women (n = 218) with low serum 25(OH)D concentrations might be beneficial. At baseline, serum 25(OH)D3 levels averaged 21.4 ng/mL (53.5 nmol/L). So they were sufficient (> 50 nmol/L) according to IOM recommendations but they spent, on average, 2.2 to 2.5 hours in the sun! This is not typical. Of course, vitamin D status could be lower because ~50% of participants reported using sunscreen as often reported for this age group. Over the course of 12 months, vitamin D dietary intake (averaging 263-364 IU/d; see Supplement 1) did not change. And, as expected, was considerably below IOM recommendations (600 IU/d). Both interventions (placebo and supplementation) had similar average weight loss over 12 months. However, women whose vitamin D status became replete with supplementation (vs those who didn't), lost more weight, had a greater waist circumference reduction, and lost a greater percent of body fat.

In an interview, Dr McTiernan, a co-author said, “This suggests women trying to lose weight might want their D levels checked by their provider and replenish vitamin D levels either through supplements or sun and then have their D levels rechecked after a few months to make sure they have risen to a healthy level.”

Thank you Dr McTiernan. Such good advice – using biological sampling to determine need, to advise on options - more sun exposure, dietary change or dietary supplementation – and to achieve optimal nutrient status. Here’s to greater adoption of biomarkers for peace of mind.

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